LIDAR Based Distance Measurements With Tiered Power Control

ABSTRACT

Methods and systems for controlling illumination power of a LIDAR based, three dimensional imaging system based on discrete illumination power tiers are described herein. In one aspect, the illumination intensity of a pulsed beam of illumination light emitted from a LIDAR system is varied in accordance with a set of illumination power tiers based on the difference between a desired and a measured return pulse. In a further aspect, the illumination power tier is selected based on whether an intensity difference exceeds one of a sequence of predetermined, tiered threshold values. In this manner, the intensity of measured return pulses is maintained within a linear range of the analog to digital converter for objects detected over a wide range of distances from the LIDAR system and a wide range of environmental conditions in the optical path between the LIDAR system and the detected object.

CROSS REFERENCE TO RELATED APPLICATION

The present application for patent claims priority under 35 U.S.C. § 119from U.S. provisional patent application Ser. No. 62/615,877 entitled“LIDAR Based Distance Measurements With Tiered Power Control,” filedJan. 10, 2018, the subject matter of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The described embodiments relate to LIDAR based 3-D point cloudmeasuring systems.

BACKGROUND INFORMATION

LIDAR systems employ pulses of light to measure distance to an objectbased on the time of flight (TOF) of each pulse of light. A pulse oflight emitted from a light source of a LIDAR system interacts with adistal object. A portion of the light reflects from the object andreturns to a detector of the LIDAR system. Based on the time elapsedbetween emission of the pulse of light and detection of the returnedpulse of light, a distance is estimated. In some examples, pulses oflight are generated by a laser emitter. The light pulses are focusedthrough a lens or lens assembly. The time it takes for a pulse of laserlight to return to a detector mounted near the emitter is measured. Adistance is derived from the time measurement with high accuracy.

Some LIDAR systems employ a single laser emitter/detector combinationcombined with a rotating mirror to effectively scan across a plane.Distance measurements performed by such a system are effectively twodimensional (i.e., planar), and the captured distance points arerendered as a 2-D (i.e. single plane) point cloud. In some examples,rotating mirrors are rotated at very fast speeds (e.g., thousands ofrevolutions per minute).

In many operational scenarios, a 3-D point cloud is required. A numberof schemes have been employed to interrogate the surrounding environmentin three dimensions. In some examples, a 2-D instrument is actuated upand down and/or back and forth, often on a gimbal. This is commonlyknown within the art as “winking” or “nodding” the sensor. Thus, asingle beam LIDAR unit can be employed to capture an entire 3-D array ofdistance points, albeit one point at a time. In a related example, aprism is employed to “divide” the laser pulse into multiple layers, eachhaving a slightly different vertical angle. This simulates the noddingeffect described above, but without actuation of the sensor itself.

In all the above examples, the light path of a single laseremitter/detector combination is somehow altered to achieve a broaderfield of view than a single sensor. The number of pixels such devicescan generate per unit time is inherently limited due limitations on thepulse repetition rate of a single laser. Any alteration of the beampath, whether it is by mirror, prism, or actuation of the device thatachieves a larger coverage area comes at a cost of decreased point clouddensity.

As noted above, 3-D point cloud systems exist in several configurations.However, in many applications it is necessary to see over a broad fieldof view. For example, in an autonomous vehicle application, the verticalfield of view should extend down as close as possible to see the groundin front of the vehicle. In addition, the vertical field of view shouldextend above the horizon, in the event the car enters a dip in the road.In addition, it is necessary to have a minimum of delay between theactions happening in the real world and the imaging of those actions. Insome examples, it is desirable to provide a complete image update atleast five times per second. To address these requirements, a 3-D LIDARsystem has been developed that includes an array of multiple laseremitters and detectors. This system is described in U.S. Pat. No.7,969,558 issued on Jun. 28, 2011, the subject matter of which isincorporated herein by reference in its entirety.

In many applications, a sequence of pulses is emitted. The direction ofeach pulse is sequentially varied in rapid succession. In theseexamples, a distance measurement associated with each individual pulsecan be considered a pixel, and a collection of pixels emitted andcaptured in rapid succession (i.e., “point cloud”) can be rendered as animage or analyzed for other reasons (e.g., detecting obstacles). In someexamples, viewing software is employed to render the resulting pointclouds as images that appear three dimensional to a user. Differentschemes can be used to depict the distance measurements as 3-D imagesthat appear as if they were captured by a live action camera.

Existing LIDAR systems employ a beam of light to interrogate aparticular volume of the surrounding environment at any given time. Thedetection of return signals includes significant sources of measurementnoise that are exacerbated as measurement ranges are extended. In manyapplications, the signal to noise ratio of measured signals is improvedby increasing laser pulse intensity. However, increased laser pulseintensity may result in saturation of the detector, signal conditioningelectronics, analog-to-digital converters, or any combination thereof,particularly for short range measurements.

Improvements in power control of LIDAR systems are desired, whilemaintaining high levels of imaging resolution and range.

SUMMARY

Methods and systems for controlling illumination power of a LIDAR based,three dimensional imaging system based on discrete illumination powertiers are described herein.

In one aspect, the illumination intensity of a pulsed beam ofillumination light emitted from a LIDAR system is varied based on theintensity of measured return pulses. In this manner, the intensity ofmeasured return pulses is maintained within a linear range of the ADCfor objects detected over a wide range of distances from the LIDARsystem and a wide range of environmental conditions in the optical pathbetween the LIDAR system and the detected object. By maintaining theintensity of measured return pulses within the linear range of the ADC,both low signal to noise ratio and saturation are avoided.

In some embodiments, an illumination power control module generates acontrol signal based on a difference between a desired intensity leveland a measured intensity level. The control signal is communicated to anillumination driver IC that causes the illumination driver IC to changethe intensity of the illumination generated by an illumination sourcefrom one discrete illumination power level to another. In theseembodiments, the control signal is a digital signal indicative of adesired illumination power level.

In another aspect, an illumination power control module determines thedesired illumination power level based on whether an intensitydifference exceeds one of a sequence of predetermined, tiered thresholdvalues.

The values of the intensity difference thresholds are predeterminedvalues (i.e., values are known before the determination of thedifference between the desired and measured return pulse intensity). Insome embodiments, the value of each intensity difference threshold isstored in a look-up table. In some embodiments, the value of eachintensity difference threshold is characterized by a nonlinear function.In some embodiments, the value of each intensity difference thresholddepends on the current power level. In some embodiments, the values ofeach intensity difference threshold vary by a fixed scaling factor. Insome embodiments, the value of the each intensity difference thresholddepends on whether the difference between the desired and measuredreturn intensity signals is positive or negative.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not limiting in any way. Other aspects,inventive features, and advantages of the devices and/or processesdescribed herein will become apparent in the non-limiting detaileddescription set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrative of an operational scenario including aLIDAR based, three dimensional imaging system 120 configured toimplement tiered illumination power control in one embodiment.

FIG. 2 is a diagram illustrative of the timing associated with theemission of a measurement pulse from an integrated LIDAR measurementdevice 130 and capture of the returning measurement pulse.

FIG. 3 is a simplified diagram illustrative of return signal intensityas a function of distance between a LIDAR system and the target undermeasurement for four different illumination power levels.

FIGS. 4A-4D depict an illustration of an illumination power controlscheme based on predetermined, threshold values in one embodiment.

FIG. 5 depicts a simplified diagram illustrative of three segments of apulse firing signal generated by controller 140 that is periodic withperiod, T_(p).

FIG. 6 is a simplified diagram illustrative of the timing of lightemission from each of sixteen integrated LIDAR measurement devices.

FIG. 7 is a diagram illustrative of an embodiment of a 3-D LIDAR system100 configured to implement tiered illumination power control.

FIG. 8 is a diagram illustrative of another embodiment of a 3-D LIDARsystem 10 configured to implement tiered illumination power control.

FIG. 9 is a diagram illustrative of an exploded view of 3-D LIDAR system100 in one exemplary embodiment.

FIG. 10 depicts a view of optical elements 116 in greater detail.

FIG. 11 depicts a cutaway view of optics 116 to illustrate the shapingof each beam of collected light 118.

FIG. 12 depicts a flowchart illustrative of a method 200 of performing aLIDAR measurement by an integrated LIDAR measurement device implementingtiered illumination power control in at least one novel aspect.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

FIG. 1 depicts a LIDAR measurement system 120 in one embodiment. LIDARmeasurement system 120 includes a master controller 190 and one or moreintegrated LIDAR measurement devices 130. An integrated LIDARmeasurement device 130 includes a return signal receiver integratedcircuit (IC) 150, an illumination driver integrated circuit (IC) 140, anillumination source 132, a photodetector 138, and a trans-impedanceamplifier (TIA) 141. In the embodiment depicted in FIG. 1, each of theseelements is mounted to a common substrate 144 (e.g., printed circuitboard) that provides mechanical support and electrical connectivityamong the elements.

In addition, in some embodiments, an integrated LIDAR measurement deviceincludes one or more voltage supplies that provide voltage to theelectronic elements mounted to substrate 144 and electrical power to theillumination source 132. The voltage supplies may be configured tosupply any suitable voltage. In some embodiments, one or more of thevoltage supplies are mounted to substrate 144. However, in general, anyof the voltage supplies described herein may be mounted to a separatesubstrate and electrically coupled to the various elements mounted tosubstrate 144 in any suitable manner.

Master controller 190 is configured to generate a pulse command signal191 that is communicated to receiver IC 150 of integrated LIDARmeasurement device 130. In general, a LIDAR measurement system includesa number of different integrated LIDAR measurement devices 130. In theseembodiments, master controller 190 communicates a pulse command signal191 to each different integrated LIDAR measurement device. In thismanner, master controller 190 coordinates the timing of LIDARmeasurements performed by any number of integrated LIDAR measurementdevices.

Pulse command signal 191 is a digital signal generated by mastercontroller 190. Thus, the timing of pulse command signal 191 isdetermined by a clock associated with master controller 190. In someembodiments, the pulse command signal 191 is directly used to triggerpulse generation by illumination driver IC 140 and data acquisition byreceiver IC 150. However, illumination driver IC 140 and receiver IC 150do not share the same clock as master controller 190. For this reason,precise estimation of time of flight becomes much more computationallytedious when the pulse command signal 191 is directly used to triggerpulse generation and data acquisition.

In the depicted embodiment, receiver IC 150 receives pulse commandsignal 191 and generates a pulse trigger signal, V_(TRG) 143, inresponse to the pulse command signal 191. Pulse trigger signal 143 iscommunicated to illumination driver IC 140 and directly triggersillumination driver IC 140 to provide an electrical pulse 131 toillumination source 132, which causes illumination source 132 togenerate a pulse of illumination light 134. In addition, pulse triggersignal 143 directly triggers data acquisition of return signal 142 andassociated time of flight calculation. In this manner, pulse triggersignal 143 generated based on the internal clock of receiver IC 150 isemployed to trigger both pulse generation and return pulse dataacquisition. This ensures precise synchronization of pulse generationand return pulse acquisition which enables precise time of flightcalculations.

Illumination source 132 emits a measurement pulse of illumination light134 in response to a pulse of electrical current 131. The illuminationlight 134 is focused and projected onto a particular location in thesurrounding environment by one or more optical elements of the LIDARsystem.

In some embodiments, the illumination source 132 is laser based (e.g.,laser diode). In some embodiments, the illumination source is based onone or more light emitting diodes. In general, any suitable pulsedillumination source may be contemplated.

As depicted in FIG. 1, illumination light 134 emitted from integratedLIDAR measurement device 130 and corresponding return measurement light135 reflected back toward integrated LIDAR measurement device 130 sharea common optical path. Integrated LIDAR measurement device 130 includesa photodetector 138 having an active sensor area 137. As depicted inFIG. 1, illumination source 132 is located outside the field of view ofthe active area 137 of the photodetector. As depicted in FIG. 1, anovermold lens 136 is mounted over the photodetector 138. The overmoldlens 136 includes a conical cavity that corresponds with the rayacceptance cone of return light 135. Illumination light 134 fromillumination source 132 is injected into the detector reception cone bya fiber waveguide. An optical coupler optically couples illuminationsource 132 with the fiber waveguide. At the end of the fiber waveguide,a mirror element 133 is oriented at an angle (e.g., 45 degrees) withrespect to the waveguide to inject the illumination light 134 into thecone of return light 135. In one embodiment, the end faces of the fiberwaveguide are cut at a 45 degree angle and the end faces are coated witha highly reflective dielectric coating to provide a mirror surface. Insome embodiments, the waveguide includes a rectangular shaped glass coreand a polymer cladding of lower index of refraction. In someembodiments, the entire optical assembly is encapsulated with a materialhaving an index of refraction that closely matches the index ofrefraction of the polymer cladding. In this manner, the waveguideinjects the illumination light 134 into the acceptance cone of returnlight 135 with minimal occlusion.

The placement of the waveguide within the acceptance cone of the returnlight 135 projected onto the active sensing area 137 of detector 138 isselected to ensure that the illumination spot and the detector field ofview have maximum overlap in the far field.

As depicted in FIG. 1, return light 135 reflected from the surroundingenvironment is detected by photodetector 138. In some embodiments,photodetector 138 is an avalanche photodiode. Photodetector 138generates an output signal 139 that is received and amplified by TIA141. The amplified return signal 142 is communicated to return signalanalysis module 160. In general, the amplification of output signal 139may include multiple, amplifier stages. In this sense, an analogtrans-impedance amplifier is provided by way of non-limiting example, asmany other analog signal amplification schemes may be contemplatedwithin the scope of this patent document. Although TIA 141 is integratedwith return signal receiver IC 150 as depicted in FIG. 1, in general,TIA 141 may be implemented as a discrete device separate from thereceiver IC 150. In some embodiments, it is preferable to integrate TIA141 with receiver IC 150 to save space and reduce signal contamination.

Return signal receiver IC 150 is a mixed analog/digital signalprocessing IC. In the embodiment depicted in FIG. 1, return signalreceiver IC 150 includes TIA 141, a return signal analysis module 160, atime of flight calculation module 159, an illumination power controlmodule 170, and an analog to digital conversion module 158.

Return signal receiver IC 150 performs several functions. In theembodiment depicted in FIG. 1, receiver IC 150 identifies one or morereturn pulses of light reflected from one or more objects in thesurrounding environment in response to the pulse of illumination light134, and determines a time of flight associated with each of thesereturn pulses. In general, the output signal 139 is processed by returnsignal receiver IC 150 for a period of time that corresponds with thetime of flight of light from the LIDAR measurement device 130 to adistance equal to the maximum range of the device 130, and back to thedevice 130. During this period of time, the illumination pulse 134 mayencounter several objects at different distances from the integratedLIDAR measurement device 130. Thus, output signal 139 may includeseveral pulses, each corresponding to a portion of the illumination beam134 reflected from different reflective surfaces located at differentdistances from device 130. In another aspect, receiver IC 150 determinesvarious properties of each of the return pulses. As depicted in FIG. 1,return signal analysis module 160 determines an indication of a width ofeach return pulse, V_(WIDTH) 157, determines the peak amplitude of eachreturn pulse, V_(PEAK) 156, and samples each return pulse waveformindividually over a sampling window that includes the peak amplitude ofeach return pulse waveform, V_(WIND) 155. These signal properties andtiming information are converted to digital signals by ADC 158 andcommunicated to illumination power control module 170 and to mastercontroller 190. Master controller 190 may further process this data, orcommunicate this data directly to an external computing device forfurther image processing (e.g., by a user of the LIDAR measurementsystem 120).

FIG. 2 depicts an illustration of the timing associated with theemission of a measurement pulse from an integrated LIDAR measurementdevice 130 and capture of the returning measurement pulse. As depictedin FIG. 2, a measurement is initiated by the rising edge of pulsetrigger signal 143 generated by receiver IC 150. As depicted in FIGS. 1and 2, an amplified, return signal 142 is generated by TIA 141. Asdescribed hereinbefore, a measurement window (i.e., a period of timeover which collected return signal data is associated with a particularmeasurement pulse) is initiated by enabling data acquisition at therising edge of pulse trigger signal 143. Receiver IC 150 controls theduration of the measurement window, T_(measurement), to correspond withthe window of time when a return signal is expected in response to theemission of a measurement pulse sequence. In some examples, themeasurement window is enabled at the rising edge of pulse trigger signal143 and is disabled at a time corresponding to the time of flight oflight over a distance that is approximately twice the range of the LIDARsystem. In this manner, the measurement window is open to collect returnlight from objects adjacent to the LIDAR system (i.e., negligible timeof flight) to objects that are located at the maximum range of the LIDARsystem. In this manner, all other light that cannot possibly contributeto useful return signal is rejected.

As depicted in FIG. 2, return signal 142 includes three returnmeasurement pulses that correspond with the emitted measurement pulse.In general, signal detection is performed on all detected measurementpulses. In one example, signal analysis may be performed to identify theclosest valid signal 142B (i.e., first valid instance of the returnmeasurement pulse), the strongest signal, and the furthest valid signal142C (i.e., last valid instance of the return measurement pulse in themeasurement window). Any of these instances may be reported aspotentially valid distance measurements by the LIDAR system.

Internal system delays associated with emission of light from the LIDARsystem (e.g., signal communication delays and latency associated withthe switching elements, energy storage elements, and pulsed lightemitting device) and delays associated with collecting light andgenerating signals indicative of the collected light (e.g., amplifierlatency, analog-digital conversion delay, etc.) contribute to errors inthe estimation of the time of flight of a measurement pulse of light.Thus, measurement of time of flight based on the elapsed time betweenthe rising edge of the pulse trigger signal 143 and each valid returnpulse (i.e., 142B and 142C) introduces undesirable measurement error. Insome embodiments, a calibrated, pre-determined delay time is employed tocompensate for the electronic delays to arrive at a corrected estimateof the actual optical time of flight. However, the accuracy of a staticcorrection to dynamically changing electronic delays is limited.Although, frequent re-calibrations may be employed, this comes at a costof computational complexity and may interfere with system up-time.

In the depicted embodiment, receiver IC 150 measures time of flightbased on the time elapsed between the detection of a detected pulse 142Adue to internal cross-talk between the illumination source 132 andphotodetector 138 and a valid return pulse (e.g., 142B and 142C). Inthis manner, systematic delays are eliminated from the estimation oftime of flight. Pulse 142A is generated by internal cross-talk witheffectively no distance of light propagation. Thus, the delay in timefrom the rising edge of the pulse trigger signal and the instance ofdetection of pulse 142A captures all of the systematic delays associatedwith illumination and signal detection. By measuring the time of flightof valid return pulses (e.g., return pulses 142B and 142C) withreference to detected pulse 142A, all of the systematic delaysassociated with illumination and signal detection due to internalcross-talk are eliminated. As depicted in FIG. 2, receiver IC 150estimates the time of flight, TOF₁, associated with return pulse 142Band the time of flight, TOF₂, associated with return pulse 142C withreference to return pulse 142A.

In some embodiments, the signal analysis is performed by receiver IC150, entirely. In these embodiments, time of flight signals 192communicated from integrated LIDAR measurement device 130 include anindication of the time of flight of each return pulse determined byreceiver IC 150. In some embodiments, signals 155-157 include waveforminformation associated with each return pulse generated by receiver IC150. This waveform information may be processed further by one or moreprocessors located on board the 3-D LIDAR system, or external to the 3-DLIDAR system to arrive at another estimate of distance, an estimate ofone of more physical properties of the detected object, or a combinationthereof.

In one aspect, the illumination intensity of a pulsed beam ofillumination light emitted from a LIDAR system is varied based on theintensity of measured return pulses. In this manner, the intensity ofmeasured return pulses is maintained within a linear range of the ADCfor objects detected over a wide range of distances from the LIDARsystem and a wide range of environmental conditions in the optical pathbetween the LIDAR system and the detected object. By maintaining theintensity of measured return pulses within the linear range of the ADC,both low signal to noise ratio and saturation are avoided.

FIG. 3 depicts an illustrative plot of return signal intensity as afunction of distance between a LIDAR system and the target undermeasurement for four different illumination power levels 175A-D. Asillustrated in FIG. 3, the return signal intensity is an 8-bit digitalvalue indicative of the intensity of the measured return signal 139.However, in general, the return signal intensity may be characterized byany suitable digital or analog signal.

As illustrated in FIG. 3, the range of measurement distances that fallwithin a linear range of the measurement system varies depending onillumination power level. For example, as illustrated in FIG. 3,plotline 175A characterizes the response of the LIDAR measurement systemat a relatively high power level. At this power level, a high signal tonoise ratio (e.g., signal intensity greater than fifty) is expected atmeasurement distances between 200 meters and 160 meters. However, atdistances below 160 meters, the LIDAR measurement system saturates. Atreduced power levels 175B, 175C, and 175D, the LIDAR system saturates atprogressively smaller distances, but at a cost of reduced signal tonoise ratio (i.e., reduced signal intensity) for a given distance.

The intensity of the return signal may be determined in many differentways. In the embodiment depicted in FIG. 1, return signal analysismodule 160 determines a width of each return pulse, V_(WIDTH) 157, apeak amplitude of each return pulse, V_(PEAK) 156, and a sampling windowthat includes the peak amplitude of each return pulse waveform, V_(WIND)155. These signal properties and timing information are converted todigital signals by ADC 158 and communicated to illumination powercontrol module 170. In one embodiment, illumination power control module170 determines the intensity of the return signal as the peak amplitudeof each return pulse, V_(PEAK) 156. In another embodiment, illuminationpower control module 170 determines the intensity of the return signalas the average value of the peak amplitude of each return pulse withinsampling window, V_(WIND) 155. In another embodiment, illumination powercontrol module 170 determines the intensity of the return signal as themean value of the peak amplitude of each return pulse within samplingwindow, V_(WIND) 155. In another embodiment, illumination power controlmodule 170 determines the intensity of the return signal as acombination of a peak value, V_(PEAK) 156, and pulse width, V_(WIDTH)157 associated with each return pulse. In general, any suitableindication of the intensity of the return signal 139 may be contemplatedwithin the scope of this patent document.

In some other embodiments, return signal analysis module 160communicates values of any of V_(WIDTH) 157, V_(PEAK) 156, and V_(WIND)155 as analog signals (without conversion by ADC 158). In theseembodiments, illumination power control module 170 determines thedesired illumination power level based on the analog signals.

An exemplary measurement 176 of intensity, I_(MEAS), of a return signalis depicted in FIG. 3. As depicted in FIG. 3, the measured intensity,I_(MEAS), is significantly lower than a desired intensity level,I_(DES). In the example depicted in FIG. 3, the desired intensity levelis near the middle of the range of ADC 158 (i.e., digital signal valueof 100).

In one aspect, illumination power control module 170 generates a controlsignal, V_(CTL) 171, based on the difference, I_(DIFF), between thedesired intensity level, I_(DES), and the measured intensity level,I_(MEAS). V_(CTL), 171 is communicated to illumination driver IC 140 andcauses illumination driver IC 140 to increase the intensity of theillumination beam 134 generated by illumination source 132 from theillumination power level associated with plotline 175D to a higherillumination power level associated with plotline 175B. As depicted inFIG. 3, the expected measured intensity 177 at the higher power level ismuch closer to the desired intensity level.

In one embodiment, V_(CTL) 171 is a digital signal indicative of adesired illumination power level. In this embodiment, illuminationdriver IC 140 adjusts the illumination power level to the desired powerlevel in response to the value of V_(CTL) 171. In one embodiment,V_(CTL) 171 is a 4-bit digital number that indicates any of sixteendifferent power levels depending on the value of V_(CTL) 171. However,in general, any number of different, discrete illumination power levelsmay be considered within the scope of this patent document.

In another aspect, illumination power control module 170 determines thedesired illumination power level based on whether the intensitydifference, I_(DIFF), exceeds one of a sequence of predetermined, tieredthreshold values.

FIGS. 4A-4D depict an illustration of an illumination power controlscheme based on predetermined, threshold values in one embodiment. Inthe example depicted in FIGS. 4A-4D, a LIDAR measurement system includesfour illumination power levels, L1, L2, L3, and L4 in order ofincreasing illumination power. In one example, L1 (lowest power level)corresponds to system response curve 175D depicted in FIG. 3, L2corresponds to system response curve 175C, L3 corresponds to systemresponse curve 175B, and L4 corresponds to system response curve 175A.

As depicted in FIG. 4A, if the difference between a desired intensity ofthe return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L1-L2), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171, that causes illumination driver 140 to increase illumination powerfrom L1 to L2. Similarly, if the difference between a desired intensityof the return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L1-L3), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171 that causes illumination driver 140 to increase illumination powerfrom L1 to L3. Similarly, if the difference between a desired intensityof the return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L1-L4), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171 that causes illumination driver 140 to increase illumination powerfrom L1 to L4.

As depicted in FIG. 4B, if the difference between a desired intensity ofthe return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L2-L3), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171, that causes illumination driver 140 to increase illumination powerfrom L2 to L3. Similarly, if the difference between a desired intensityof the return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L2-L4), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171 that causes illumination driver 140 to increase illumination powerfrom L2 to L4. Similarly, if the difference between a desired intensityof the return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L2-L1), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171 that causes illumination driver 140 to decrease illumination powerfrom L2 to L1.

As depicted in FIG. 4C, if the difference between a desired intensity ofthe return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L3-L4), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171, that causes illumination driver 140 to increase illumination powerfrom L3 to L4. Similarly, if the difference between a desired intensityof the return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L3-L2), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171 that causes illumination driver 140 to decrease illumination powerfrom L3 to L2. Similarly, if the difference between a desired intensityof the return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L3-L1), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171 that causes illumination driver 140 to decrease illumination powerfrom L3 to L1.

As depicted in FIG. 4D, if the difference between a desired intensity ofthe return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L4-L3), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171 that causes illumination driver 140 to decrease illumination powerfrom L4 to L3. Similarly, if the difference between a desired intensityof the return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L4-L2), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171 that causes illumination driver 140 to increase illumination powerfrom L4 to L2. Similarly, if the difference between a desired intensityof the return signal and the measured intensity of the return signalexceeds an intensity difference threshold, IDT_(L4-L1), illuminationpower control module 170 communicates a value of control signal, V_(CTL)171, that causes illumination driver 140 to increase illumination powerfrom L4 to L1.

The values of the intensity difference thresholds are predeterminedvalues (i.e., values are known before the determination of thedifference between the desired and measured return pulse intensity). Insome embodiments, the value of each intensity difference threshold isstored in a look-up table. In some embodiments, the value of eachintensity difference threshold is characterized by a nonlinear function.In some embodiments, the value of each intensity difference thresholddepends on the current power level. In some embodiments, the values ofeach intensity difference threshold vary by a fixed scaling factor. Insome embodiments, the value of the each intensity difference thresholddepends on whether the difference between the desired and measuredreturn intensity signals is positive or negative.

In the embodiment depicted in FIG. 1, illumination power control module170 generates a digital signal V_(CTL) 171 to communicate a desiredillumination power level to illumination driver IC 140. However, in someother embodiments, illumination power control module 170 generates oneor more analog signals that are communicated to illumination driver IC140 that cause illumination driver IC 140 to generate illuminationpulses 134 at the desired illumination power level. In one example,illumination power control module 170 communicates an analog amplitudecontrol signal, V_(AMP), to illumination driver IC 140. In response,illumination driver IC 140 changes the pulse amplitude based on thereceived value of V_(AMP). In another example, illumination powercontrol module 170 communicates an analog amplitude control signal,V_(PWC), to illumination driver IC 140. In response, illumination driverIC 140 changes the illumination pulse duration based on the receivedvalue of V_(PWC).

FIG. 5 depicts three segments of a pulse firing signal generated bycontroller 140 that is periodic with period, T_(p). In segment 167A, thepulse intensity for six consecutive pulses is held steady at a mediumvalue. In segment, 167B, the pulse intensity alternates between a highintensity setting and a low intensity setting for six consecutivepulses. In segment 167C, the pulse intensity is held high for one pulse,then low for two subsequent pulses for ten consecutive pulses. Ingeneral, a LIDAR system may be configured to vary the pulse intensity inany desired manner on a pulse by pulse basis or in groups of pulses tomaintain the intensity of the return signal within a linear range of theLIDAR measurement system.

In a further embodiment, a LIDAR system, such as LIDAR system 10depicted in FIG. 8, includes a number of integrated LIDAR measurementdevices operating in coordination with a common controller (e.g.,controller 190). FIG. 6 depicts an exemplary diagram 195 illustratingthe timing of light emission from each of the sixteen integrated LIDARmeasurement devices. In another further aspect, the repetitive patternof pulses of illumination light emitted from each pulsed illuminationsystem is independently controllable. Thus, the repetition patternassociated with each pulsed illumination system can be independentlycontrolled.

As depicted in FIG. 6, a measurement pulse sequence is emitted from afirst integrated LIDAR measurement device. After a delay time,T_(DELAY), a measurement pulse sequence is emitted from a secondintegrated LIDAR measurement device. In this manner a sequence ofsixteen measurement pulses are emitted in different directions from theLIDAR device during a measurement period, T_(MEASUREMENT). The energystorage elements associated with each of the sixteen pulsed illuminationsystems are charged after the measurement period for a charging period,T_(CHARGE). After, the charging period, another measurement pulsesequence is emitted from each pulsed illumination system over asubsequent measurement period.

In some embodiments, the delay time is set to be greater than the timeof flight of the measurement pulse sequence to and from an objectlocated at the maximum range of the LIDAR device. In this manner, thereis no cross-talk among any of the sixteen pulsed illumination systems.

In some other embodiments, a measurement pulse may be emitted from onepulsed illumination system before a measurement pulse emitted fromanother pulsed illumination system has had time to return to the LIDARdevice. In some of these embodiments, care is taken to ensure that thereis sufficient spatial separation between the areas of the surroundingenvironment interrogated by each beam to avoid cross-talk.

In another aspect, a master controller is configured to generate aplurality of pulse command signals, each communicated to a differentintegrated LIDAR measurement device. Each return pulse receiver ICgenerates a corresponding pulse control signal based on the receivedpulse command signal.

FIGS. 7-9 depict 3-D LIDAR systems that include multiple integratedLIDAR measurement devices. In some embodiments, a delay time is setbetween the firing of each integrated LIDAR measurement device. In someexamples, the delay time is greater than the time of flight of themeasurement pulse sequence to and from an object located at the maximumrange of the LIDAR device. In this manner, there is no cross-talk amongany of the integrated LIDAR measurement devices. In some other examples,a measurement pulse is emitted from one integrated LIDAR measurementdevice before a measurement pulse emitted from another integrated LIDARmeasurement device has had time to return to the LIDAR device. In theseembodiments, care is taken to ensure that there is sufficient spatialseparation between the areas of the surrounding environment interrogatedby each beam to avoid cross-talk.

FIG. 7 is a diagram illustrative of an embodiment of a 3-D LIDAR system100 in one exemplary operational scenario. 3-D LIDAR system 100 includesa lower housing 101 and an upper housing 102 that includes a domed shellelement 103 constructed from a material that is transparent to infraredlight (e.g., light having a wavelength within the spectral range of 700to 1,700 nanometers). In one example, domed shell element 103 istransparent to light having a wavelengths centered at 905 nanometers.

As depicted in FIG. 7, a plurality of beams of light 105 are emittedfrom 3-D LIDAR system 100 through domed shell element 103 over anangular range, a, measured from a central axis 104. In the embodimentdepicted in FIG. 7, each beam of light is projected onto a plane definedby the x and y axes at a plurality of different locations spaced apartfrom one another. For example, beam 106 is projected onto the xy planeat location 107.

In the embodiment depicted in FIG. 7, 3-D LIDAR system 100 is configuredto scan each of the plurality of beams of light 105 about central axis104. Each beam of light projected onto the xy plane traces a circularpattern centered about the intersection point of the central axis 104and the xy plane. For example, over time, beam 106 projected onto the xyplane traces out a circular trajectory 108 centered about central axis104.

FIG. 8 is a diagram illustrative of another embodiment of a 3-D LIDARsystem 10 in one exemplary operational scenario. 3-D LIDAR system 10includes a lower housing 11 and an upper housing 12 that includes acylindrical shell element 13 constructed from a material that istransparent to infrared light (e.g., light having a wavelength withinthe spectral range of 700 to 1,700 nanometers). In one example,cylindrical shell element 13 is transparent to light having awavelengths centered at 905 nanometers.

As depicted in FIG. 8, a plurality of beams of light 15 are emitted from3-D LIDAR system 10 through cylindrical shell element 13 over an angularrange, β. In the embodiment depicted in FIG. 8, the chief ray of eachbeam of light is illustrated. Each beam of light is projected outwardinto the surrounding environment in a plurality of different directions.For example, beam 16 is projected onto location 17 in the surroundingenvironment. In some embodiments, each beam of light emitted from system10 diverges slightly. In one example, a beam of light emitted fromsystem 10 illuminates a spot size of 20 centimeters in diameter at adistance of 100 meters from system 10. In this manner, each beam ofillumination light is a cone of illumination light emitted from system10.

In the embodiment depicted in FIG. 8, 3-D LIDAR system 10 is configuredto scan each of the plurality of beams of light 15 about central axis14. For purposes of illustration, beams of light 15 are illustrated inone angular orientation relative to a non-rotating coordinate frame of3-D LIDAR system 10 and beams of light 15′ are illustrated in anotherangular orientation relative to the non-rotating coordinate frame. Asthe beams of light 15 rotate about central axis 14, each beam of lightprojected into the surrounding environment (e.g., each cone ofillumination light associated with each beam) illuminates a volume ofthe environment corresponding the cone shaped illumination beam as it isswept around central axis 14.

FIG. 9 depicts an exploded view of 3-D LIDAR system 100 in one exemplaryembodiment. 3-D LIDAR system 100 further includes a lightemission/collection engine 112 that rotates about central axis 104. Inthe embodiment depicted in FIG. 9, a central optical axis 117 of lightemission/collection engine 112 is tilted at an angle, θ, with respect tocentral axis 104. As depicted in FIG. 9, 3-D LIDAR system 100 includes astationary electronics board 110 mounted in a fixed position withrespect to lower housing 101. Rotating electronics board 111 is disposedabove stationary electronics board 110 and is configured to rotate withrespect to stationary electronics board 110 at a predeterminedrotational velocity (e.g., more than 200 revolutions per minute).Electrical power signals and electronic signals are communicated betweenstationary electronics board 110 and rotating electronics board 111 overone or more transformer, capacitive, or optical elements, resulting in acontactless transmission of these signals. Light emission/collectionengine 112 is fixedly positioned with respect to the rotatingelectronics board 111, and thus rotates about central axis 104 at thepredetermined angular velocity, w.

As depicted in FIG. 9, light emission/collection engine 112 includes anarray of integrated LIDAR measurement devices 113. In one aspect, eachintegrated LIDAR measurement device includes a light emitting element, alight detecting element, and associated control and signal conditioningelectronics integrated onto a common substrate (e.g., printed circuitboard or other electrical circuit board).

Light emitted from each integrated LIDAR measurement device passesthrough a series of optical elements 116 that collimate the emittedlight to generate a beam of illumination light projected from the 3-DLIDAR system into the environment. In this manner, an array of beams oflight 105, each emitted from a different LIDAR measurement device areemitted from 3-D LIDAR system 100 as depicted in FIG. 9. In general, anynumber of LIDAR measurement devices can be arranged to simultaneouslyemit any number of light beams from 3-D LIDAR system 100. Lightreflected from an object in the environment due to its illumination by aparticular LIDAR measurement device is collected by optical elements116. The collected light passes through optical elements 116 where it isfocused onto the detecting element of the same, particular LIDARmeasurement device. In this manner, collected light associated with theillumination of different portions of the environment by illuminationgenerated by different LIDAR measurement devices is separately focusedonto the detector of each corresponding LIDAR measurement device.

FIG. 10 depicts a view of optical elements 116 in greater detail. Asdepicted in FIG. 10, optical elements 116 include four lens elements116A-D arranged to focus collected light 118 onto each detector of thearray of integrated LIDAR measurement devices 113. In the embodimentdepicted in FIG. 10, light passing through optics 116 is reflected frommirror 124 and is directed onto each detector of the array of integratedLIDAR measurement devices 113. In some embodiments, one or more of theoptical elements 116 is constructed from one or more materials thatabsorb light outside of a predetermined wavelength range. Thepredetermined wavelength range includes the wavelengths of light emittedby the array of integrated LIDAR measurement devices 113. In oneexample, one or more of the lens elements are constructed from a plasticmaterial that includes a colorant additive to absorb light havingwavelengths less than infrared light generated by each of the array ofintegrated LIDAR measurement devices 113. In one example, the colorantis Epolight 7276A available from Aako BV (The Netherlands). In general,any number of different colorants can be added to any of the plasticlens elements of optics 116 to filter out undesired spectra.

FIG. 11 depicts a cutaway view of optics 116 to illustrate the shapingof each beam of collected light 118.

In this manner, a LIDAR system, such as 3-D LIDAR system 10 depicted inFIG. 8, and system 100, depicted in FIG. 7, includes a plurality ofintegrated LIDAR measurement devices each emitting a pulsed beam ofillumination light from the LIDAR device into the surroundingenvironment and measuring return light reflected from objects in thesurrounding environment.

In some embodiments, such as the embodiments described with reference toFIG. 7 and FIG. 8, an array of integrated LIDAR measurement devices ismounted to a rotating frame of the LIDAR device. This rotating framerotates with respect to a base frame of the LIDAR device. However, ingeneral, an array of integrated LIDAR measurement devices may be movablein any suitable manner (e.g., gimbal, pan/tilt, etc.) or fixed withrespect to a base frame of the LIDAR device.

In some other embodiments, each integrated LIDAR measurement deviceincludes a beam directing element (e.g., a scanning mirror, MEMS mirroretc.) that scans the illumination beam generated by the integrated LIDARmeasurement device.

In some other embodiments, two or more integrated LIDAR measurementdevices each emit a beam of illumination light toward a scanning mirrordevice (e.g., MEMS mirror) that reflects the beams into the surroundingenvironment in different directions.

In a further aspect, one or more integrated LIDAR measurement devicesare in optical communication with an optical phase modulation devicethat directs the illumination beam(s) generated by the one or moreintegrated LIDAR measurement devices in different directions. Theoptical phase modulation device is an active device that receives acontrol signal that causes the optical phase modulation device to changestate and thus change the direction of light diffracted from the opticalphase modulation device. In this manner, the illumination beam(s)generated by the one or more integrated LIDAR devices are scannedthrough a number of different orientations and effectively interrogatethe surrounding 3-D environment under measurement. The diffracted beamsprojected into the surrounding environment interact with objects in theenvironment. Each respective integrated LIDAR measurement devicemeasures the distance between the LIDAR measurement system and thedetected object based on return light collected from the object. Theoptical phase modulation device is disposed in the optical path betweenthe integrated LIDAR measurement device and an object under measurementin the surrounding environment. Thus, both illumination light andcorresponding return light pass through the optical phase modulationdevice.

FIG. 12 illustrates a flowchart of a method 200 suitable forimplementation by a LIDAR measurement system as described herein. Insome embodiments, LIDAR measurement systems 10, 100, and 120 areoperable in accordance with method 200 illustrated in FIG. 23. However,in general, the execution of method 200 is not limited to theembodiments of LIDAR measurement systems 10, 100, and 120 described withreference to FIGS. 8, 7, and 1, respectively. These illustrations andcorresponding explanation are provided by way of example as many otherembodiments and operational examples may be contemplated.

In block 201, a pulse of illumination light is emitted from a pulsedillumination source of a LIDAR measurement device into a threedimensional environment in response to a first amount of electricalpower.

In block 202, one of at least three different, selectable amounts ofelectrical power is provided to the pulsed illumination source at aparticular time. The first amount of electrical power is a first of theat least three different, selectable amounts of electrical power.

In block 203, an amount of light reflected from the three dimensionalenvironment illuminated by the pulse of illumination light is detected.

In block 204, a return measurement signal indicative of the detectedamount of light is generated.

In block 205, the return measurement signal indicative of the detectedamount of light is received.

In block 206, an indication of an intensity of the return measurementsignal is determined.

In block 207, a difference between the intensity of the output signaland a desired intensity of the output signal is determined.

In block 208, a control command is communicated to the illuminationdriver that causes the illumination driver to select any of the at leastthree different, selectable amounts of electrical power based on thedifference between the intensity of the return measurement signal andthe desired intensity.

In general, the terms “integrated circuit,” “master controller,” and“computing system” may be broadly defined to encompass any device havingone or more processors, which execute instructions from a memory medium.

Master controller 190 or any external computing system may include, butis not limited to, a personal computer system, mainframe computersystem, workstation, image computer, parallel processor, or any otherdevice known in the art.

It should be recognized that various steps described throughout thepresent disclosure may be carried out by return signal receiver IC 150,illumination driver IC 140, master controller 190, or another computersystem. Moreover, different subsystems of the LIDAR measurement system120, may include a computer system suitable for carrying out at least aportion of the steps described herein. Therefore, the aforementioneddescription should not be interpreted as a limitation on the presentinvention but merely an illustration.

In one example, program instructions 292 implementing methods such asthose described herein may be transmitted over a transmission mediumsuch as a wire, cable, or wireless transmission link. For example, asillustrated in FIG. 1, program instructions 292 stored in memory 291 aretransmitted to processor 295 over bus 294. Program instructions 292 arestored in a computer readable medium (e.g., memory 291). Exemplarycomputer-readable media include read-only memory, a random accessmemory, a magnetic or optical disk, or a magnetic tape.

As depicted in FIG. 1, program instructions 292, memory 291, processor295, and bus 294 are implemented as part of master controller 190.However, in other examples, program instructions implementing methodssuch as those described herein, memory, one or more processors, and abus are implemented as part of return signal receiver IC 150. In someexamples, program instructions implementing methods such as thosedescribed herein, memory, one or more processors, and a bus are alsoimplemented as part of illumination driver IC 140.

In general, return signal receiver IC 150, illumination driver IC 140,and master controller 190 may be communicatively coupled to otherdevices in any manner known in the art. For example, the mastercontroller 190 may be coupled to the return signal receiver IC 150associated with an integrated LIDAR measurement device 130.

Master controller 190 may be configured to receive and/or acquire dataor information from an integrated LIDAR measurement device 130 by atransmission medium that may include wireline and/or wireless portions.In this manner, the transmission medium may serve as a data link betweenthe master controller 190 and other subsystems of the LIDAR measurementsystem 120.

Master controller 190 may be configured to receive and/or acquire dataor information (e.g., LIDAR measurement results, compressed data sets,segmented data sets, feature sets, etc.) from other systems by atransmission medium that may include wireline and/or wireless portions.In this manner, the transmission medium may serve as a data link betweenthe master controller 190 and other systems (e.g., memory on-board LIDARmeasurement system 120, external memory, or external systems). Forexample, the master controller 190 may be configured to communicatemeasurement data 293 (e.g., LIDAR image information 105) from a storagemedium (i.e., memory 291) to an external computing system via a datalink. Moreover, the master controller 190 may receive data from othersystems via a transmission medium. For instance, feature maps andlocation information determined by master controller 190 may be storedin a permanent or semi-permanent memory device (e.g., memory 291). Inthis regard, measurement results may be exported to another system.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A light detection and ranging (LIDAR) device, comprising: a pulsed illumination source emitting a pulse of illumination light from the LIDAR device into a three dimensional environment in response to a first amount of electrical power; an illumination driver configured to provide one of at least three different, selectable amounts of electrical power to the pulsed illumination source at a particular time, wherein the first amount of electrical power is a first of the at least three different, selectable amounts of electrical power; a photosensitive detector that detects an amount of light reflected from the three dimensional environment illuminated by the pulse of illumination light and generates a return measurement signal indicative of the detected amount of light; and a computing system configured to: receive the return measurement signal indicative of the detected amount of light; determine an indication of an intensity of the return measurement signal; determine a difference between the intensity of the output signal and a desired intensity of the output signal; and communicate a control command to the illumination driver that causes the illumination driver to select any of the at least three different, selectable amounts of electrical power based on the difference between the intensity of the return measurement signal and the desired intensity.
 2. The LIDAR device of claim 1, wherein a second of the at least three different, selectable amounts of electrical power exceeds the first amount of electrical power, and wherein a third of the at least three different, selectable amounts of electrical power exceeds the second amount of electrical power, and wherein the control command causes the illumination driver to select the second amount of electrical power when the difference between the intensity of the output signal and the desired intensity exceeds a first predetermined threshold value, and wherein the control command causes the illumination driver to select the third amount of electrical power when the difference between the intensity of the output signal and the desired intensity exceeds a second predetermined threshold value.
 3. The LIDAR device of claim 2, wherein the values of the first and second threshold values depend on the first amount of electrical power.
 4. The LIDAR device of claim 2, wherein the first and second threshold values vary by a fixed scaling factor.
 5. The LIDAR device of claim 2, wherein first and second threshold values depend on whether the difference between the intensity of the output signal and the desired intensity is a positive value or a negative value.
 6. The LIDAR device of claim 2, wherein the first and second threshold values are characterized by a nonlinear function.
 7. The LIDAR device of claim 2, wherein the return measurement signal includes one or more return measurement pulses, and wherein the indication of the intensity of the return measurement signal is a peak value of the one or more return measurement pulses.
 8. The LIDAR device of claim 2, wherein the return measurement signal includes one or more return measurement pulses, and wherein the indication of the intensity of the return measurement signal is an average value or a mean value of the one or more return measurement pulses.
 9. A LIDAR measurement system, comprising: a pulsed illumination source emitting a pulse of illumination light from the LIDAR device into a three dimensional environment in response to a first amount of electrical power; an illumination driver configured to provide one of at least three different, selectable amounts of electrical power to the pulsed illumination source at a particular time, wherein the first amount of electrical power is a first of the at least three different, selectable amounts of electrical power; a photosensitive detector that detects an amount of light reflected from the three dimensional environment illuminated by the pulse of illumination light and generates a return measurement signal indicative of the detected amount of light; and computer-readable instructions stored on a non-transitory, computer-readable medium, the computer-readable instructions comprising: code for causing a computing system to receive the return measurement signal indicative of the detected amount of light; code for causing the computing system to determine an indication of an intensity of the return measurement signal; code for causing the computing system to determine a difference between the intensity of the output signal and a desired intensity of the output signal; and code for causing the computing system to communicate a control command to the illumination driver that causes the illumination driver to select any of the at least three different, selectable amounts of electrical power based on the difference between the intensity of the return measurement signal and the desired intensity.
 10. The LIDAR measurement system of claim 9, wherein a second of the at least three different, selectable amounts of electrical power exceeds the first amount of electrical power, and wherein a third of the at least three different, selectable amounts of electrical power exceeds the second amount of electrical power, and wherein the control command causes the illumination driver to select the second amount of electrical power when the difference between the intensity of the output signal and the desired intensity exceeds a first predetermined threshold value, and wherein the control command causes the illumination driver to select the third amount of electrical power when the difference between the intensity of the output signal and the desired intensity exceeds a second predetermined threshold value.
 11. The LIDAR measurement system of claim 10, wherein the values of the first and second threshold values depend on the first amount of electrical power.
 12. The LIDAR measurement system of claim 10, wherein the first and second threshold values vary by a fixed scaling factor.
 13. The LIDAR measurement system of claim 10, wherein first and second threshold values depend on whether the difference between the intensity of the output signal and the desired intensity is a positive value or a negative value.
 14. The LIDAR measurement system of claim 10, wherein the first and second threshold values are characterized by a nonlinear function.
 15. The LIDAR measurement system of claim 10, wherein the return measurement signal includes one or more return measurement pulses, and wherein the indication of the intensity of the return measurement signal is a peak value of the one or more return measurement pulses.
 16. The LIDAR measurement system of claim 10, wherein the return measurement signal includes one or more return measurement pulses, and wherein the indication of the intensity of the return measurement signal is an average value or a mean value of the one or more return measurement pulses.
 17. A method comprising: emitting a pulse of illumination light from a pulsed illumination source of a LIDAR measurement device into a three dimensional environment in response to a first amount of electrical power; providing one of at least three different, selectable amounts of electrical power to the pulsed illumination source at a particular time, wherein the first amount of electrical power is a first of the at least three different, selectable amounts of electrical power; detecting an amount of light reflected from the three dimensional environment illuminated by the pulse of illumination light; generating a return measurement signal indicative of the detected amount of light; receiving the return measurement signal indicative of the detected amount of light; determining an indication of an intensity of the return measurement signal; determining a difference between the intensity of the output signal and a desired intensity of the output signal; and communicating a control command to the illumination driver that causes the illumination driver to select any of the at least three different, selectable amounts of electrical power based on the difference between the intensity of the return measurement signal and the desired intensity.
 18. The method of claim 17, wherein a second of the at least three different, selectable amounts of electrical power exceeds the first amount of electrical power, and wherein a third of the at least three different, selectable amounts of electrical power exceeds the second amount of electrical power, and wherein the control command causes the illumination driver to select the second amount of electrical power when the difference between the intensity of the output signal and the desired intensity exceeds a first predetermined threshold value, and wherein the control command causes the illumination driver to select the third amount of electrical power when the difference between the intensity of the output signal and the desired intensity exceeds a second predetermined threshold value.
 19. The method of claim 18, wherein first and second threshold values depend on whether the difference between the intensity of the output signal and the desired intensity is a positive value or a negative value.
 20. The method of claim 18, wherein the return measurement signal includes one or more return measurement pulses, and wherein the indication of the intensity of the return measurement signal is a peak value, and average value, or a mean value of the one or more return measurement pulses. 